Esters of Azodicarboxylic Acid

The cycloadducts 257 of esters of azodicarboxylic acid to 2,7-dimethyloxepin undergo a spontaneous Claisen rearrangement to form the dihydrocyclopropapyridazines 258 (equation 139)132. Homofulvenes 259 (R1, R2 = HorMe) react with dimethyl azodicarboxylate to form rearranged adducts 260 (equation 140)133. 

C. Heteroatomic dienophiles 111 Esters of azodicarboxylic acid 12k 4-Phenyl-l,2,4-triazoline-3,5-dione 131 hninocarbamates... 

We were not able to obtain any cycloadduct from unactivated 2-azadienes 139 and esters of acetylenedicarboxylic acid. However, we found that 139 did cycloadd to typical electron-poor dienophiles such as esters of azodicarboxylic acid and tetracyanoethylene (Scheme 62). Thus, diethyl and diisopropyl azodicarboxylates underwent a concerted [4 + 2] cycloaddition with 139 to afford in a stereoselective manner triazines 278 in 85-90% yield (86CC1179). The minor reaction-rate variations observed with the solvent polarity excluded zwitterionic intermediates on the other hand, AS was calculated to be 48.1 cal K 1 mol-1 in CC14, a value which is in the range of a concerted [4 + 2] cycloaddition. Azadienes 139 again reacted at room temperature with the cyclic azo derivative 4-phenyl-1,2,4-triazoline-3,5-dione, leading stereoselectively to bicyclic derivatives 279... 

Esters of Azodicarboxylic Acid. These compounds are versatile aminating reagents for alkyl- (see Eq. 46), allenyl- (see Eq. 59), aryl- and heteroarylmetal (see Eq. 75) derivatives, and especially enolates (see Eqs. 87, 88, 115-117, and... 

Preparation of Alkyl Hydrazines. As mentioned previously (Eq. 19), additions of aliphatic carbanions to unactivated azo compounds are rare. Another example is shown in Eq. 43.208 On the other hand, additions to diaryl azo compounds (Eq. 44)211 and esters of azodicarboxylic acids (Eq. 46)358 are well documented. The intermediate anion in Eq. 44 can be trapped with alkyl halides to give tetrasubstituted hydrazines. An extension of the reaction of Eq. 44 exploits the ready displacement of the benzotriazole functionality by Grignard reagents (Eq. 45).359 Because of the instability of the intermediate 45, the Grignard reagent is added before the azobenzene in the actual experiments. 

Huisgen, R., Pohl, H. Addition reactions of the N,N-double bond. III. The reaction of azodicarboxylic acid ester with olefins. Chem. Ber. 

Mitsunobu, O., Yamada, M., Mukaiyama, T. Preparation of esters of phosphoric acid by the reaction of trivalent phosphorus compounds with diethyl azodicarboxylate in the presence of alcohols. Bull. Chem. Soc. Jpn. 1967,40, 935-939. 

The tetraphenyl ester of azodiphosphonic acid is a more reactive dienophile than diethyl azodicarboxylate. Because of its instability it is prepared from... 

Esterification.—An alternative to the well-known azodicarboxylate-PhsP esterification procedure has dimethyl mesoxalate as proton acceptor. Yields of esters of benzoic acid are quite good (50—86%), and the reaction results in complete configurational inversion of the alcohol component. Isocyanides have also been shown to be useful dehydrating reagents in this type of reaction. Esterification of acids with one equivalent of an alcohol can be achieved by prior reaction of the acid with 2-halopyridinium salts. cf. refs. 134—140). An overall conversion of amines into acetates and benzoates (Scheme 29) involves conversion... 

In a 1-1., three-necked, round-bottomed flask equipped with a constant-pressure dropping funnel, a mechanical stirrer, and a reflux condenser is placed 174 g. (1.0 mole) of ethyl azodicarbox-ylate in 150 ml. of ether. Freshly prepared cyclopentadiene (70 g., 1.06 moles) is added dropwise over a 1-hour period to the stirred ethereal solution of diethyl azodicarboxylate. During the addition a gentle reflux is maintained by external cooling with an ice-water bath as needed. When the addition is complete, the reaction mixture is allowed to stand for 4 hours, or less if the yellow color of the azodicarboxylic acid ester disappears. I he dropping funnel and condenser are replaced by a glass stoj)pcr and a short distillation head, respectively. The ether and unreactcd diene are distilled off on a steam bath and the... 

In common with other azodicarboxylic acid derivatives, the uses of 4-phenyl-l,2,4-triazoline-3,5-dione are many. It undergoes a Diels-Alder reaction with most dienes11-14 and is, in fact, the most reactive dienophile so far reported.15 16 As with the formation of all Diels-Alder adducts the reaction is reversible, and in the case of the adduct with 3-j3-acetoxy-17-cyano-5,14,16-androstatriene, the reverse reaction can be made to proceed under especially mild conditions.14 An instance has also been reported of the dione photochemically catalyzing other retro Diels-Alder reactions.17 Along with the proven use of azodicarboxylic ester,18-18 the dione should be potentially important in the preparation of strained ring compounds. 

This method is based on the activation of one cysteine peptide as a sulfenohydrazide derivative by the reaction of the free thiol group of the cysteine peptide with azodicarboxylic acid as a dialkyl ester or dimorpholide depending on the solubility requirements.156 Following the isolation and characterization of the S-activated intermediate, reaction with a second free thiol cysteine component via thiolysis leads to the desired intermolecular disulfide bond, as shown in Scheme 4. 

The photochemical addition of 2H-azirines to the carbonyl group of aldehydes, ketones and esters is completely regiospecific (77H143). Besides the formation of the isomeric oxazolines 18 from 3 and ethyl cyanoformate, there is also formed the imidazole 19 from addition to the C = N in the expected regioselective manner. Thioesters lead to thiazolines 20, while isocyanates and ketenes produce heterocycles 21 (Scheme 4). The photocycloaddition of arylazirines with a variety of multiple bonds proceeds in high yield and provides a convenient route for the synthesis of five-membered heterocyclic rings. Some of the dipolarophiles include azodicarboxylates, acid chlorides, vinylphospho-nium salts and p-quinones. 

The Mitsunobu esterification of carboxylic acids with alcohols in the presence of Ph3P and DEAD (diethyl azodicarboxylate) occurs under neutral conditions and provides the corresponding esters in high yields. 

Imino ethers and 2-alkoxybenzthiazolium salts prepared from chiral alcohols react with carboxylic acids to give the esters of the corresponding inverted rdcohols (Scheme 39).7ic.72d,73,75a reaction of a chiral alcohol with a carboxylic acid, DEAD and PhsP affords the ester of the inverted alcohol (Scheme 44). 2 Diisopropyl or dimethyl azodicarboxylate can be used instead of DEAD. Little difference between these reagents has been reported. ... 

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